[]string, []int16, []int32, []int64, []int, []uint16, []uint32,
[]uint64, []uint, []float32, and []float64 are now supported in the
simple protocol like they are in the normal usage of the extended
protocol.
This allows handling queries where it is unknown if there will be a
result set or not. If it is not a result set returning query the
command tag will still be available.
It was a mistake to use it in other contexts. This made interop
difficult between pacakges that depended on pgtype such as pgx and
packages that did not like pgconn and pgproto3. In particular this was
awkward for prepared statements.
This is preparation for removing pgx.PreparedStatement in favor of
pgconn.PreparedStatement.
It is impossible to guarantee that the a query executed with the simple
protocol will behave the same as with the extended protocol. This is
because the normal pgx path relies on knowing the OID of query
parameters. Without this encoding a value can only be determined by the
value instead of the combination of value and PostgreSQL type. For
example, how should a []int32 be encoded? It might be encoded into a
PostgreSQL int4[] or json.
Removal also simplifies the core query path.
The primary reason for the simple protocol is for servers like PgBouncer
that may not be able to support normal prepared statements. After
further research it appears that issuing a "flush" instead "sync" after
preparing the unnamed statement would allow PgBouncer to work.
The one round trip mode can be better handled with prepared statements.
As a last resort, all original server functionality can still be accessed by
dropping down to PgConn.
Previously, a failed connection could be put back in a pool and when the
next query was attempted it would fail immediately trying to prepare the
query or reset the deadline. It wasn't clear if the Query or Exec call
could safely be retried since there was no way to know where it failed.
You can now call LastQuerySent and if it returns false then you're
guaranteed that the last call to Query(Ex)/Exec(Ex) didn't get far enough
to attempt to send the query. The call can be retried with a new
connection.
This is used in the stdlib to return a ErrBadConn if a network error
occurred and the statement was not attempted.
Fixes#427
Bug was chooseParameterFormatCode would see that type could handle
binary format so binary format would be chosen. But
encodePreparedStatementArgument would see driver.Valuer first and
would encode with that -- which is text mode. So the server would
receive a text format value when expecting a binary format value.
Discovered while investigating #316
Since QueryRow delegates to Query, it needs Query to always return
non-nil *Rows to prevent a nil pointer deference when the QueryRow
caller calls Scan(). This commit fixes the few returns in QueryEx that
return nil on errors rather than *Rows with its err field set.
